1. Field of the Invention
The invention generally relates to a light source device and a planar light source device used in a liquid crystal display (LCD) device.
2. Prior Art
In general, an LCD device has the advantages of thinness, light weight, and low power consumption. For this reason, LCD devices are widely utilized in various types of electronic equipment, from pocket calculators to large-scale office automation equipment.
Conventionally, planar light source devices are designed for use in an LCD device for backlighting purposes. The planar light source device generally includes a light guide plate (LGP) and at least one light source. The LGP has at least one light incidence surface, and one light-emitting surface. In operation, light rays emitted by the light source(s) enter the LGP through the light incident surface(s) thereof, and are guided through the LGP to emit from the light-emitting surface. Each light source may be a linear light source or a point light source. The point light source is generally a light emitting diode (LED), which emits light rays over a region subtending an angle of about 140°. Generally, a plurality of LEDs is arranged adjacent to the light incident surface(s) of the LGP to ensure high illuminance and high uniformity of light emitting from the light-emitting surface. This kind of light source device is disclosed in U.S. Pat. No. 6,386,720 issued on May 14, 2002.
However, the lighting characteristics of ordinary LEDs are limited, and the uniformity of illumination of the planar light source device may not be sufficient. Referring to FIG. 10, a conventional planar light source device 1 utilizes two LEDs 11, 12 as light sources to illuminate an LGP 10. Each of the LEDs 11, 12 emits light rays over a region subtending an angle of about 140°. As seen, some dark regions (“shadows”) A, B, C are created on a light-emitting surface of the LGP 10, because few light rays reach these regions. The number of LEDs 11, 12 can be increased to diminish the shadows A, B, C. However, this is achieved at the cost of supplying more LEDs 11, 12 and having higher power consumption.